The present invention relates generally to turbofan aircraft gas turbine engines, and, more specifically, to noise attenuation therein.
In an aircraft turbofan engine, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gases which flow downstream through turbine stages that extract energy therefrom. A high pressure turbine powers the compressor, and a low pressure turbine powers a fan disposed upstream of the compressor.
The combustion gases are discharged from the core engine through an annular exhaust nozzle, and the fan air is discharged through another exhaust nozzle surrounding the core engine. The majority of propulsion thrust is provided by the pressurized fan air discharged from the fan exhaust nozzle, and remaining thrust is provided from the combustion gases discharged from the core exhaust nozzle.
The core exhaust flow is discharged from the core nozzle at high velocity and then mixes with the high velocity fan air discharged from the fan nozzle as well as with ambient air through which the engine and aircraft travel. The high velocity exhaust flow generates significant noise during operation, with additional noise being generated by the fan exhaust, as well as by the rotating components of the engine.
Turbofan aircraft engines have various designs including low bypass, high bypass, and long or short duct nacelles. And, these various designs may include various features for attenuating noise corresponding with the specific noise source. However, noise attenuation features typically add weight to the engine, and it is desirable to minimize engine weight in an aircraft turbofan engine.
The noise sources in a typical turbofan engine include both the velocity of the fan discharge stream itself, and mechanical noise due to rotation of the engine rotor components during operation. The large fan blades must be rotated at suitable rotational speeds at which tip speeds range from subsonic through transonic and even supersonic. The fan blades therefore generate a significant component of noise during operation.
However, attenuation of exhaust noise or mechanical noise of the fan typically requires different solutions specific thereto.
Accordingly, it is desired to provide an aircraft turbofan engine with an improved fan exhaust nozzle for specifically attenuating fan noise due to discharge velocity of the fan exhaust during takeoff operation.
A turbofan exhaust nozzle includes a fan duct defined between a fan nacelle and a core engine cowling. The fan duct includes a longitudinal endwall and a partition spaced therefrom to define a secondary flow duct. The fan duct also includes a primary outlet, and the secondary duct includes a secondary outlet. The partition between the two ducts includes an aperture covered by a selectively movable flap.